Antenna system and feeder



Patented Apr. 8, 1941 ANTENNA SYSTEM AND FEEDER Hans Otto Roosenstein, Berlin-Tempelhof, Germany, assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application April 29, 1939, Serial N o. 270,783 In Germany May 14, 1938 7 Claims.

This invention concerns a shielded antenna lead, especially for short-wave work in which disturbances which are occasioned by reaction of the antenna upon the outer sheath or cover of the lead are avoided. In the operation of antenna leads which are surrounded by shielding means disturbing actions have been noticed,` and these have been ascribed to the fact that the radio frequency currents flowing on the inside or inner surface of the lead shielding are able to reach the outer surface of the shielding over the edge at the antenna end of the shielding where they cause an antenna action just as the antenna itself which will disturb and interfere with the antenna field and thus render the shielding effect illusory. One could think of diminishing such disturbing actions by lining or coating the outside of the shielding means with a material of low electrical conductivity. However, this merely has the effect of the major part of the radio frequency current avoiding such lining just because it presents a high resistance` and thus be compelled to continue to ilow below the shielding surface with low incidental attenuation on the shielding. A reduction of the antenna effect of the shielding would thus not be secured.

According to the invention, the damping on the outer surface of the shielding is essentially increased by surrounding the shielding at or near the end adjoining the antenna with one or several ccaxially mounted cylinders insulated from one another and consisting of material possessing high electric loss, preferably a magnetic material.

The invention shall now be explained in more detail by reference to the following description, which is accompanied by a drawing wherein Figs. 1, 2 and 3 illustrate three different embodiments of the invention.

Referring to Fig. l in more detail, l denotes the inner conductor of the antenna lead or cable which is surrounded by the outer conductor 2. At the antenna end of the outer conductor, as before indicated, the currents flowing on the inner surface of the outer conductor are able to reach the outer surface thereof over the edge of the outer conductor, as indicated by the arrows. But if, as here disclosed and suggested, a coainal cylinder 3 insulated from the outer conductor and made, say, of ferromagnetic material is provided at or in the neighborhood of the end of the shielding, then, due to the current upon the outer surface of conductor 2 a current will now over the inner surface of the cylinder 3; and this current will reach the outer surface thereof over the edges of the same and thus flow around the cylinder 3. Inasmuch as the material of cylinder 3 possesses extremely high damping for radio frequency currents, it follows that the radio frequency current on cylinder 3 and thus also the current on the shield 2 will be effectively attenuated. Instead of using only one cylinder 3, it will be understood that also several such cylinders could be used as shown in Fig. 2. Referring to this Fig. 2 in more detail, l again is the inner conductor, 2 the outer conductor of the antenna lead or cable, while 3, 4, 5, 6, l are the various cylinders being insulated from one another and consisting of ferromagnetic material. The length of the various cylinders could be so much more reduced, the greater the number of such cylinders. 'I'he cylinders, for instance, could consist of wrapped iron ribbon or tape. It will be obvious that thorough and careful insulation between the various iron bands is indispensable in this embodiment because the current always has a tendency naturally to nd the shortest path around the cylindrical wrap presenting a minimum of attenuation. However, in the presence of multiple subdivision, as represented in Fig. 2, a current will flow around each cylinder which is equal to the current flowing on the outside of sheath or shell 2, with the result that the losses by Wrapping a relatively great length of band or tape can be raised to such a degree that practically complete destruction of the radio frequency current occurs.

In an arrangement as shown in Fig. 2, of course, there still exists a risk of the antenna capacitively transferring potentials over the damping collar to the portion of conductor located below the collar. However, such actions may be readily suppressed by disposing a second collar at a distance other than one-half wavelength and amounting preferably to an odd multiple of quarter wavelengths, as shown in Fig. 3. Inasmuch as the portion of conductor between the two collar-like structures is no longer capable of resonance, the attenuation which is obtained will be of a maximum value. Moreover, the use of a counterpoise in the form of a planar conductor united with the end of the outer conductor will be found of advantage.

Manufacture of the damping or attenuator means may be facilitated by using, in lieu of the cylindrical bodies or structures which consist of sheet strips placed in superposed relation, iron in the form of insulated wire, for instance, is employed as a basis, this wire being Wrapped ball-fashion at the desired places along the conductor arrangement.

If .several sheet-metal cylinders shifted one over the other are used, the effect thereof may be increased by increasing the surface area thereof, say, by circular or spiral grooves or furrows. An identical effect is obtainable by a chemical treatment of the cylinder so applied that it will attack the surface thereof irregularly. If the permeability of the iron cylinders is not unduly reduced, it is finally feasible to reduce the surface conductivity thereof by forming the surface layer of a mixture of nely divided iron and a semi-conductor material.

What is claimed is:

1. In combination, an antenna, a. coaxial feeder having an inner conductor and an outer shell, its inner conductor being connected to said antenna, and a hollow metallic tube surrounding the outer shell of said feeder for a portion near its end adjacent said antenna, said tube being insulated from said outer shell and consisting of magnetic material to produce high electric loss in the outer surface of said feeder.

2. In combination, an antenna, a coaxial feeder having an inner conductor and an outer shell, the inner conductor of said feeder being connected to said antenna, and a plurality of concentric hollcw metallic tubes surrounding the outer shell of said feeder for a portion near its end adjacent said antenna, said tubes being insulated from said outer shell and each other and consisting of magnetic material to produce high electric loss in the outer surface of said feeder.

3. In combination, an antenna, a coaxial feeder having an inner conductor and an outer shell, the inner conductor of said feeder being connected to said antenna, and a plurality of concentric hollow metallic tubes surrounding the outer shell of said feeder fo-r a portion near its end adjacent said antenna, said tubes being insulated from said outer shell and each other and consisting of magnetic material to produce high electric loss in the outer surface of said feeder,

the lengths of said plurality of hollow metallic tubes being inversely proportional to their number.

4. In combination, an antenna, a coaxial feeder having an inner conductor and an outer shell, and having its inner conductor connected to said antenna, a plurality of hollow metallic tubes surrounding the outer shell of said feeder near the end adjacent said antenna, said tubes being spaced along said feeder a distance other than half the length of the operating wave of said antenna, said tubes being insulated from said outer shell and consisting of magnetic material to produce high electric loss in the outer surface of said feeder.

5. In combination, an antenna, a coaxial feeder having an inner conductor and an outer shell,

. the inner conductor of said feeder being connected to said antenna, and a plurality of concentric hollow metallic tubes surrounding the outer shell of said feeder for a portion near its end adjacent said antenna, said tubes being insulated from said outer shell and each other.

6. In combination, Ian antenna, a coaxial feeder having an inner conductor and an outer shell, the inner conductor of said feeder being connected to said antenna, and a plurality of concentric hollow metallic tubes surrounding the outer shell of said feeder for a portion near its end adjacent said antenna, said tubes being insulated from said outer shell and each other, the lengths of said plurality of hollow metallic tubes being inversely proportional to their number.

7. In combination, an antenna, a coaxial feeder having an inner conductor and an outer shell, and having its inner conductor connected to said antenna, a plurality of hollow metallic tubes surrounding the outer shell of said feeder near the end adjacent said antenna, said tubes being spaced along `said feeder a distance other than half the length of the operating wave of said antenna, said tubes being insulated from said outer shell.

HANS OTTO ROOSENS'I'EIN. 

